A-Level Biology OCR A
Dna Bases Terminator Strand Fragments Sequencing Nucleotides Single
DNA sequencing involves mixing DNA with primers, nucleotides, and terminator bases, followed by temperature cycling to create fragments of varying lengths. Capillary sequencing separates these fragments by size, using fluorescent markers to identify each base, and computers reassemble the genome.
DNA sequencing involves mixing DNA with primers, nucleotides, and terminator bases, followed by temperature cycling to create fragments of varying lengths. Capillary sequencing separates these fragments by size, using fluorescent markers to identify each base, and computers reassemble the genome.
| Front |
Describe the steps in DNA sequencing (capillary method). |
| Back |
DNA sequencing:- DNA mixed with a primer (DNA polymerase) & an excess of nucleotides & terminator bases
- Mixture is placed under rapidly changing temperatures to split up the molecule into single strands & at 60*C, DNA polymerase starts to build up new DNA strands by adding nucleotides with complementary bases to the single strand DNA template
- Each time a terminator base is added, the synthesis is terminated
- Since there are lower amounts of terminator bases present & they are added at random - many DNA fragments of different lengths form & after many cycles, all possible DNA chains will be produced with the reaction stopped at every base
- The DNA fragments are separated according to their length by capillary sequencing, fluorescent markers are used to identify the final base on each fragment
- Order of bases in capillary tubes shows the sequence of the new, complementary strand of DNA that was made - this used to build up sequence of original DNA strand
- Computers reassemble genomes by comparing all fragments and finding areas of overlap between them
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A-Level Biology OCR A